The present invention relates to a north seeking gyro, or gyro compass, and course holding, or directional, gyro arrangement for a vehicle.
Arrangements of this type generally include
(1) a gyro with a normally horizontal rotor axis and an inner gimbal supporting the gyro rotor and having an axis which is vertical in the north seeking mode, a deflection of the inner gimbal from a given position against a restraint being possible and a pickup being provided to generate a signal in dependence on such deflection; PA1 (2) a second gimbal in which the inner gimbal is mounted and which has a pivot axis that extends parallel to the rotor axis when the latter is in its undeflected position; PA1 (3) an outer gimbal in which the second gimbal is mounted and which is mounted to pivot about an axis which is approximately parallel to the normally vertical upright axis of the vehicle; PA1 (4) a follow-up device for the outer gimbal which, based on the signal from the pickup disposed between the inner gimbal and the second gimbal, causes the outer gimbal to follow the inner gimbal and is provided with a drive to selectively pivot the second gimbal about its axis either into the position where the axis of the inner gimbal is in a vertical position, when the gyro is to operate as a gyro compass, or into another position where the axis is essentially inclined to the vertical, when the gyro is to operate as a directional gyro.
Such a gyro is disclosed in German Patent No. 1,265,998 and counterpart U.S. Pat. No. 3,394,596. In the operation of the gyro described therein, it is assumed that the axis of the outer gimbal is vertical, and the axis of a second intermediate gimbal is then also vertical when in the north seeking mode and the rotor axis and the tilt axis of a first intermediate gimbal are horizontal. In order to make possible such vertical alignment of the axis of the outer gimbal it is proposed in that patent to use a gyro stabilized platform, which makes the device more expensive.
In the known gyro arrangement, the second intermediate gimbal, when its axis is in the vertical position--i.e. in the north seeking mode--is deflected with respect to the first intermediate gimbal by the north driving moment and, with the aid of the thus obtained pickup voltage, the outer gimbal is rotated until there no longer is a deflection, i.e. the rotor axis has been aligned with the north direction. Then the first intermediate gimbal is tilted by 90.degree. about the second axis of rotation so that the gyro becomes a directional gyro.
Due to the necessity of employing an expensive device to keep the gyro in vertical alignment, this known gyro arrangement, although actually advantageous, has not been able to find acceptance. At present the custom is still to use two separate gyros which are separately cardanically suspended. When the vehicle is in a position other than one in which its upright direction is vertical, the north seeking gyro will seek north correctly but this north value is transferred to the directional gyro with a cardanic error.